(1) Field of the Invention
The present invention relates to the manufacture of books and particularly to the movement of book blocks between successive stations of a book binding apparatus. More specifically, this invention is directed to a book block transport system and especially to book block gripping mechanisms for use in such a transport system. Accordingly, the general objects of the present invention are to provide novel and improved methods and apparatus of such character.
(2) Description of the Prior Art
In the manufacturer of books it is common practice to transport the assemblied book blocks between work stations by means of a transport system which comprises a plurality of book block gripping mechanisms. These block gripping mechanisms are continuously moved along a closed orbital track. During transport the book blocks are held between a stationary jaw, which is a flat plate-like member, and a movable jaw. The jaws are mounted from a supporting frame which is coupled to a transport chain. The movable jaw of the book block gripping mechanism will be located at the end of a pivot arm, the axis about which this arm pivots being generally parallel to the stationary clamping jaw. The opening and closing of the movable jaw is controlled by a cam and cam follower arrangement with the motion of the cam follower being transmitted to the pivot arm via a force transmission lever. A spring element will be located between the force transmission lever and the pivot arm in order to transmit the clamping force. The spring element is employed to provide compensation for variations in block thickness.
German Pat. No. 2,725,416 discloses a book block transport system of the type generally described above wherein a torsion bar spring is employed as the spring element. This torsion bar spring transmits the clamping force from the cam follower to the movable jaw and provides compensation for varying block thicknesses without requiring adjustment of the transport system.
In the transport system of the referenced German patent, in order to have adequate clamping force when the block thickness is small, the torsion spring is preloaded in such a way that the supporting tubes which receive the ends of the spring are twisted through a defined angle with respect to each other. Nevertheless, the spring characteristic is linear, as is also the case when tension or compression springs are employed to develop the clamping force for the movable jaw, and thus the actual clamping force applied to the book block is proportional to block thickness. Accordingly, in the region of work stations, additional force must be applied to the movable jaw in order to insure that the book block is not moved out of position or actually torn from between the jaws.
Because of space and cost considerations, the above-discussed problem of a clamping force which decreases as book block thickness decrease can not be satisfactorily solved merely by resort to the use of larger springs.